Jantaras

Hello,

I want to build my first wheel. I have Campagnolo (Chorus?) rear hub and Mavic CXP 30 rim.
I want to use Sapim spokes so tried Sapim spoke calculator:
https://www.sapim.be/spoke-calculator

All measurements are quite straightforward except rim thickness. Looks like Sapim uses IRD + rim thicknes, not ERD? These CXP30 are somewhat deep rims, so I have trouble measuring thickness. As I measure from the deepest part as shown in my pictures, I get 22 mm. But the nipple will go way deeper so I believe this measturement is too long. Internet says the ERD of these rims is 588 mm. My measured IRD is 572 mm. Does it mean the thickness for Sapim calculator should be 8 mm?

An additional question: do I need something more than spokes and nipples for this rim? Velobase scanned document says something about an reinforcement eyelet in assembly kit.

Thanks for you thoughts!

mrrabbit 

Why are you doing things the hard way?

Simply grab two spokes of known length...

...assuming 12mm standard profile nipples, set to the bottom of the screwdriver flat on both spokes.

Zinch em up with an analog caliper taut...

Spoke Length + Caliper Reading + Spoke Length = Effective Rim Diameter

=8-|

davidad

Spoke calc shows 587mm for these rims. I have found his measurements reliable.

Andrew R Stewart 

I have to admit that this is the first time I have heard of rim bed thickness as a factor in calculating spoke length. Since the nipple seats on the ERD side of the rim and spoke calculators take into consideration the nipple head amount (although somewhat differently so use one calculator and create the personal preference of spoke overlap with the nipple head amount that you like) how much rim thickness is not an issue. Now what could be a rim bed thickness aspect is nipple length. The extreme is a wood rim which will need a nipple long enough to reach beyond the solid rim. Andy

Steelman54 

Agree with Andrew and really like MrRabbits way of doing that, seems quick and simple. The "aero" portion of the rim does not affect spoke length.

Jantaras

Thanks for your responses!

I haven't got any loose spokes yet, so I can't use them to measure. But I think they would measure the ERD, not the rim thickness.

Most online calculators use ERD, but looks like Sapim uses it differently. As far as I understand, the ERD is rim thickness x2 +internal rim diameter. So I think Sapim uses ERD, but it is split in 2 parts: the IRD and rim thickness. Also, Sapims calculator is very simple if one uses vintage rims (most of my rims). These deeper rims are a bit complicated.

Am I rigt calculating it in this way: my measured IRD is 572 mm. CXP30 ERD is 587 mm. So rim thickness is (587-572)/2=7,5 mm ?

davidad

To simplify this the ERD is measured from inside to inside of the spokes holes 180 degrees (diameter) apart.
I have a CXP33 rim and I get the the same ERD as the Damon Rinard spoke calc. 588mm.

I used his calculator and got 282 and 284 mm spoke lengths.

Andrew R Stewart 

7,5mm is a huge Al rim bed thickness. Huge. Maybe half that is more typical. Of course it might include a nipple ferule and Mavic did use these on some of their Aero rims. The ferules might be set into the rims or added during the build.

I suggest you get a measuring caliper and begin measuring actual dimensions and not rely on published specs. This is a well know practice for better wheel builders. Andy

Jantaras

Hello all,

an update. I ended up using the Sapim calculator, I believe I used 8 mm for rim thickness, in any case, got spoke lengths of 284 mm DS and 286 mm NDS. Used 16 mm brass nipples. Sapim spokes were out of stock, so ordered DT 1,8/1,6/1,8 spokes.
The wheel is waiting for a test of time and use, I think it is not bad, at least for my eyes and for a first build There are a lot of good tutorials on the net, I used Jim Langley's video on Youtube.
Spokes are not threaded to the end of the nipple, but quite close to it.

Andrew R Stewart 

Good job. Andy